Weaning - an important step in childhood development?

From recent reading and studying I'm beginning to think that weaning is a major time of infant development.

This loss of breast milk, may be a biological step - albeit a traumatic one - to trigger the infant to start his own immune system.

Those fed with formula, don't have this step, and never went through this, They have never developed this bio stage - of learning how to react to loss of needed fat and other concentrated nurturing (loss of breast milk). Which would force them to react by developing their own immune system.

Perhaps a big part of that would be to learn how to conserve and store fats in a healthy way when it's available, to cover times when it is scarce. Below are some of the clues that suggested this from around the web:

Notes and Quotes :==============

a. These results confirm the protective effect of breast feeding and suggest there is a vulnerable period soon after breast feeding is stopped, which may be of relevance for developing preventive strategies.http://www.ncbi.nlm.nih.gov/pubmed/8761225

b. NOTE: studies show that there is a high mortality rate among infants during weaning.

e. NOTE: this period of the development of fat rolls from 6 months and beyond is also where weaning starts. It's also where the antibiotics in the mother's breast milk begin to reduce, while the child's antibiotics begin to develop.

Children are born with all three antibodies (IGG, IGA, and IGM). Because our immune system can’t make the most important antibody, IGG, in sufficient quantity until about six months, the baby is protected by IGG antibodies passed on by its mother before birth. If the baby’s own immune system doesn’t mature at the right time, the child may start a cycle of infections. This is often called “Transient Hypogammaglobulinemia of Infancy,” transient because the child will outgrow it, usually by age two or three, and Hypogammaglobulinemia because the IGG levels are low. http://www.atlantaallergy.com/educationdetail.aspx?id=17&cat=4

f. Human milk also contains fats that are essential for the health of your baby. It is necessary for brain development, absorption of fat-soluble vitamins, and is a primary calorie source. Long chain fatty acids are needed for brain, retina, and nervous system development. They are deposited in the brain during the last trimester of pregnancy and are also found in breast milk.

g. NOTE: Surely the infant would need a way to process fats during weaning in order to continue getting the fats he needs for all the development cited above.